MicroRNAs (miRNAs) have emerged as a novel class of noncoding RNAs with tremendous biological functions. More importantly, circulating cell-free miRNAs are found in blood. In contrast to our original thought, the cell-free miRNAs are relatively stable due to binding with other materials such as exosomes in circulating blood. The studies from us and other groups have revealed that these circulating cell-free miRNAs can be used as novel biomarkers of many diseases including cancer and heart disease. However, the resources and the biological roles of these circulating cell-free miRNAs beyond biomarkers under disease conditions are currently unclear. Atherosclerosis is still the major cause of morbidity and the major cost in our healthcare system. The expression profiles, resources, and biological roles of these circulating cell-free miRNAs in atherosclerosis are currently unknown. The long-term goal of our research program is to determine the biological roles of circulating cell-free miRNAs in atherosclerosis. The goal of this R21 application is determine the potential biological roles of circulating cell-free miR-122 in atherogenesis. Our hypothesis is that the live-derived cell-free miR-122 is increased in atherosclerotic blood. The blood miR-122 is able to enter the vascular walls and vascular cells. The circulating cell-free miR-122 not only can be used as a novel biomarker for atherosclerosis, but can also play an important role in atherogenesis via its direct vascular effects. Our hypothesis is supported by our preliminary studies. We will further test our hypothesis by the following two specific aims: Aim 1 is to determine the levels of miR-122 in atherosclerotic blood, its capability to enter the vascular cells, its biological functions, and the mechanisms involved, in cultured vascular cells in vitro. Aim 2 is to determine the cell-free miR-122's capability to enter the vascular walls, the levels and expression distribution of miR-122 in atherosclerotic arteries, the biological role of miR-122 in atherogenesis, and its potential mechanisms in Apo E knockout mice in vivo. The proposed study is highly innovative. If successful, it will provide a totally new mechanism and a novel therapeutic target in atherosclerosis, and may create a novel scientific paradigm: circulating cell-free microRNAs in the pathogenesis of cardiovascular diseases. In addition, the proposed study may also provide a novel biomarker of atherosclerosis in blood.